MySQL 实例

2，一个最简单的Hello world 程序

CREATE PROCEDURE HelloWorld() 
BEGIN  
    SELECT "Hello World!";  
END;

3，变量
使用DECLARE来声明，DEFAULT赋默认值，SET赋值

DECLARE counter INT DEFAULT 0;  
SET counter = counter+1; 

4，参数
IN为默认类型，值必须在调用时指定，值不能返回（值传递）
OUT值可以返回（指针传递）
INOUT值必须在调用时指定，值可以返回
CREATE PROCEDURE test(a INT, OUT b FLOAT, INOUT c INT)


5，条件判断
IF THEN、ELSEIF、ELSE、END IF

CREATE PROCEDURE discunted_price(normal_price NUMERIC(8, 2), OUT discount_price NUMERIC(8, 2))
BEGIN
    IF (normal_price > 500) THEN
        SET discount_price = normal_price * .8;
    ELSEIF (normal_price > 100) THEN
        SET discount_price = normal_price * .9;
    ELSE
        SET discount_price = normal_price;
    END IF;
END;

6，循环
LOOP、END LOOP

CREATE PROCEDURE simple_loop(OUT counter INT)
BEGIN
    SET counter = 0;
    my_simple_loop: LOOP
        SET counter = counter+1;
        IF counter = 10 THEN
            LEAVE my_simple_loop;
        END IF;
    END LOOP my_simple_loop;
END;

WHILE DO、END WHILE

CREATE PROCEDURE simple_while(OUT counter INT)
BEGIN
    SET counter = 0;
    WHILE counter != 10 DO
        SET counter = counter+1;
    END WHILE;
END ;

REPEAT、UNTILL

CREATE PROCEDURE simple_repeat(OUT counter INT)
BEGIN
    SET counter = 0;
    REPEAT
        SET counter = counter+1;
    UNTIL counter = 10 END REPEAT;
END;

7，异常处理
如果用cursor获取SELECT语句返回的所有结果集时应该定义NOT FOUND error handler来防止存储程序提前终结
如果SQL语句可能返回constraint violation等错误时应该创建一个handler来防止程序终结


8，数据库交互
INTO用于存储单行记录的查询结果

DECLARE total_sales NUMERIC(8, 2);
SELECT SUM(sale_value) INTO total_sales FROM sales WHERE customer_id=in_customer_id;

CURSOR用于处理多行记录的查询结果

CREATE PROCEDURE cursor_example()
    READS SQL DATA
BEGIN
    DECLARE l_employee_id INT;
    DECLARE l_salary NUMERIC(8,2);
    DECLARE l_department_id INT;
    DECLARE done INT DEFAULT 0;
    DECLARE cur1 CURSOR FOR SELECT employee_id, salary, department_id FROM employees;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;

    OPEN cur1;
    emp_loop: LOOP
        FETCH cur1 INTO l_employee_id, l_salary, l_department_id;
        IF done=1 THEN
            LEAVE emp_loop;
        END IF;
    END LOOP emp_loop;
    CLOSE cur1;
END;

unbounded SELECT语句用于存储过程返回结果集

CREATE PROCEDURE sp_emps_in_dept(in_employee_id INT)
BEGIN
    SELECT employee_id, surname, firstname, address1, address2, zipcode, date_of_birth FROM employees WHERE department_id=in_employee_id;
END;

UPDATE、INSERT、DELETE、CREATE TABLE等非查询语句也可以嵌入存储过程里

CREATE PROCEDURE sp_update_salary(in_employee_id INT, in_new_salary NUMERIC(8,2))
BEGIN
    IF in_new_salary < 5000 OR in_new_salary > 500000 THEN
        SELECT "Illegal salary: salary must be between $5000 and $500, 000";
    ELSE
        UPDATE employees SET salary=in_new_salary WHERE employee_id=in_employee_id;
    END IF:
END ;

9，使用CALL调用存储程序

CREATE PROCEDURE call_example(employee_id INT, employee_type VARCHAR(20))
    NO SQL
BEGIN
    DECLARE l_bonus_amount NUMERIC(8,2);

    IF employee_type='MANAGER' THEN
        CALL calc_manager_bonus(employee_id, l_bonus_amount);
    ELSE
        CALL calc_minion_bonus(employee_id, l_bonus_amount);
    END IF;
    CALL grant_bonus(employee_id, l_bonus_amount);
END;

10，一个复杂的例子

CREATE PROCEDURE putting_it_all_together(in_department_id INT)
    MODIFIES SQL DATA
BEGIN
    DECLARE l_employee_id INT;
    DECLARE l_salary NUMERIC(8,2);
    DECLARE l_department_id INT;
    DECLARE l_new_salary NUMERIC(8,2);
    DECLARE done INT DEFAULT 0;

    DECLARE cur1 CURSOR FOR
        SELECT employee_id, salary, department_id
        FROM employees
        WHERE department_id=in_department_id;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;

    CREATE TEMPORARY TABLE IF NOT EXISTS emp_raises
        (employee_id INT, department_id INT, new_salary NUMERIC(8,2));

    OPEN cur1;
    emp_loop: LOOP
        FETCH cur1 INTO l_employee_id, l_salary, l_department_id;
        IF done=1 THEN    /* No more rows */
            LEAVE emp_loop;
        END IF;
        CALL new_salary(1_employee_id, l_new_salary); /* Get new salary */
        IF (l_new_salary <> l_salary) THEN  /* Salary changed */
            UPDATE employees
                SET salary=l_new_salary
            WHERE employee_id=l_employee_id;
            /* Keep track of changed salaries */
            INSERT INTO emp_raises(employee_id, department_id, new_salary)
                VALUES (l_employee_id, l_department_id, l_new_salary);
        END IF:
    END LOOP emp_loop;
    CLOSE cur1;
    /* Print out the changed salaries */
    SELECT employee_id, department_id, new_salary from emp_raises
        ORDER BY employee_id;
END;

11，存储方法
存储方法与存储过程的区别
1，存储方法的参数列表只允许IN类型的参数，而且没必要也不允许指定IN关键字
2，存储方法返回一个单一的值，值的类型在存储方法的头部定义
3，存储方法可以在SQL语句内部调用
4，存储方法不能返回结果集
例子：

CREATE FUNCTION f_discount_price
    (normal_price NUMERIC(8,2))
    RETURNS NUMERIC(8,2)
    DETERMINISTIC
BEGIN
    DECLARE discount_price NUMERIC(8,2);

    IF (normal_price > 500) THEN
        SET discount_price = normal_price * .8;
    ELSEIF (normal_price >100) THEN
        SET discount_price = normal_price * .9;
    ELSE
        SET discount_price = normal_price;
    END IF;

    RETURN(discount_price);
END;


12，触发器
触发器在INSERT、UPDATE或DELETE等DML语句修改数据库表时触发
触发器的典型应用场景是重要的业务逻辑、提高性能、监控表的修改等
触发器可以在DML语句执行前或后触发

CREATE TRIGGER sales_trigger
    BEFORE INSERT ON sales
    FOR EACH ROW
BEGIN
    IF NEW.sale_value > 500 THEN
        SET NEW.free_shipping = 'Y';
    ELSE
        SET NEW.free_shipping = 'N';
    END IF;

    IF NEW.sale_value > 1000 THEN
        SET NEW.discount = NEW.sale_value * .15;
    ELSE
        SET NEW.discount = 0;
    END IF;
END;